An electret is a
dielectric material which retains the polarization produced in it for a longer
time and produces the electrostatic field without any source of voltage. The
biomaterials like collagen, DNA, RNA and blood vessel walls etc possess this
property. The kidney stone mainly consists of calcium oxalate and calcium
phosphate, which are dipolar in nature. The pellet of the powdered kidney stone
was formed in a mica window and identical aluminium electrodes were prepared.
The thermal polarization was carried out by sandwiching the sample between
aluminium electrodes in electrode assembly, which was kept in digital
controlled oven. The observed behaviour of thermally stimulated current (TSC)
peak is found to be strongly dependent on annealing time, which shows the
presence of shallow and deeper traps in material. These traps are probably
formed during the crystallization of substance in kidney.

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